Method of separating krypton and xenon from air



Jan. 30, 1934.". w; DENNIS 1,945,365

METHOD OF SEPARAT ING KRYP'I'ON AND XENON FROM AIR Filed Ma 5, 19:52

INVENTOR l/a/m? pen/1i! ATTORNEYS Patented Jan. 30,1934

DIETHOD F SEPARATI ING KRYPTON AND XENON FROM AIR Wolcott Dennis,Elizabeth, N. J., assignor to Air Reduction Company, Incorporated, NewYork, N. Y., a corporation of NewYork Application May 5, 193 Serial No.609,425 v 2' Claims. (Cl. 133-3415) This invention relates to theseparation and recovery of krypton and xenon from the at-- mosphere.

In the well-known methods for recovering 5 oxygen and nitrogen from airby liquefaction and rectification, the air, after compression andcooling, is liquefied, and the vapors rising from the liquid arerectified by contact with further portions of the liquid with the objectof producing vapor consisting substantially of nitrogen and a liquidcontaining the oxygen constituent. Owing to the fact that the boilingpoints of the rare gases krypton and xenon are higher than that ofoxygen, these elements accumulate in the oxygen liquid at the bottom ofthe rectification column. Inordinary practice this liquid is evaporatedand the krypton and xenon pass ofi with the oxygen. The amount ofkrypton and xenon in the atmosphere is so small that these 2e elementsappearv merely as impurities in commercial oxygen.

It is the object of the present invention to provide a simple andeffective method of recovering a liquid concentrate relatively rich inkrypton and xenon from the liquid oxygen which accumulates at the bottomof an ordinary rectification column. The'concentrate may be vaporizedand I subjected to further purification for the purpose of providingkrypton and xenon for commercial purposes.

In carrying out the invention, any system of liquefaction andrectification may be utilized to secure the initial separation of theair into nitrogen and liquid oxygen containing krypton and s5 xenon.Several systems are well-known and are in commercial use. The recoveryof the concentrate relatively rich in krypton and xenon is accomplishedby subjecting the oxygen liquid containing krypton and xenon from thebottom of 40 the primary rectification column to an auxiliaryrectification with vapors therefrom. Owing to the diflerence in boilingpoints of oxygen and of krypton and xenon, the oxygen separates as avapor and the liquid is enriched in krypton and xenon. This liquidconcentrate, rich in krypton and xenon, is-subjected to a furtherpartial vaporization and is finally withdrawn at the end of theauxiliary rectification cycle. During this final vaporization the supplyof oxygen liquid con to tainingkrypton and xenon is cut oil. The cycleis then repeated by again introducing the supply of oxygen liquid.containing krypton and xenon to the auxiliary rectification'column.During the auxiliary rectification, a small amount of liquid 66 enrichedin krypton and xenon remains on the trays of the auxiliary rectificationcolumn, and this liquid is washed downwardly by the fresh portion of theoxygen liquid and is thus accumulated with the liquid residue which iswithdrawn from the bottom of the auxiliary rectification column at theconclusion of the auxiliary recti- 'fication cycle.

Any suitable apparatus may be employed for the purpose of the invention,and it is to be particularly understood that the invention is notlimited to. any method of effecting the initial separation of nitrogenand oxygen from the atmosphere. For the purpose of clarity, theinvention is illustrated in the accompanying drawing as embodying thewell-known Claude appa-' ratus for separating oxygen and nitrogen fromthe atmosphere. The invention will be better understood by reference tothe following description and the accompanying drawing, whichillustrates diagrammatically an apparatus suitable for the 76 practiceof the invention. I

Referring to the drawing, 5 indicates a column including a plurality oftrays 6 of the usual form, over which the liquid descends as the vaporsrise during the primary rectification. A partition '7 80 near the bottomofthe column forms, with a partition 8, separate compartments 9 and 10.A plurality of tubes 11 ,and- 12 extend through the partitions 7 and 8to a head 13. A well 14 extends through the partitions and 8 and sur-.85 rounds the lower ends of the tubes 12.

Air in the liquid and gaseous phases is sup- I plied through a pipe 15in the manner hereinafter described to the compartment 9.- g The gaseousairpasses upwardly through the tubes 11 in indirect contact with liquidwhich accumulates about the tubes, and by backward return condensation apartial separation is eflected, resulting in a liquid enriched in oxygenwhich flows downwardly into the compartment 9. This liquid. togetherwith the liquid introduced through the pipe 15, is carried upwardly by apipe -16 under control of a valve 17 and is delivered onto the trays6'at an intermediate point inthe rectification column. It flowsdownwardly over the trays in contact with vapors rising from theaccumu-.- lated liquid in the bottom of the column above the partition7. v v The imcondensed residue from the tubes 11 passes into the head 13and thence downwardly through the tubes 12 and is condensed therein to aliquid consisting of nitrogen which flows into the well 14 andthencethr'ough a-pipe 18 and valve 19 into the'top' of the column 5."This liquid nltro gen flows downwardly over the trays '6 and.

washes from the rising vapors the oxygen constituent thereof, which iscondensed and joins the downwardly flowing liquid which finallyaccumulates in the bottom of the column above the partition 7. Vaporsconsisting principally of nitrogen escape as an efiluent through a pipe20 at passing through the tubes 11 and escapes through a pipe 22 as theoxygen product of the operation.

It will be understood that the air undergoingliquefaction andrectification in the primary column 5 is first compressed and cooled inthe usual compressors and interchangers (not shown).' In the compressedand cooled state it is delivered through a pipe 23 to an exchanger 24and circulates about the tubes 25 and 26 therein, where it is cooled byheat exchange with products leaving the system. The compressed andcooled air is delivered through a pipe 27 and a portion thereof passesthrough an expansion engine 28 where-it is expanded to a lower pressureand thereby cooled. It is delivered from the expansion engine 28 through'a pipe 29 to the pipe 15 and thus enters the compartment 9 at thebottom of the primary column 5. Another portion of the compressed andcooled air passes through a pipe 30 into a liquefier 31 and about thetubes 32 and 33 therein, through which cold products of the separationare conveyed. The air at the initial pressure is thus cooled andliquefied, and the liquid escapes through a pipe 34 and valve 35 and isdelivered through the'pipe 15 to the compartment 9 at the bottom of theprimary column 5.

The nitrogen from the primary column is delivered by the pipe 20 to acompartment 36 at one end of the liquefier 31', passes through the'tubesto a storage receptacleor to the atmosphere as may be desired.

The oxygen product from the pipe 22 is 'de- 'livered by a pipe 43 to acompartment 44 .at one end of the liquefier 31 and thence through thetubes 33 to a compartment 45 at the otherend of the liquefier. It passesthrough a pipe 46'to a compartment 4'? at one end or the exchanger 24,and thence through the tubes 26 to a compartment'48 at the opposite endof the exchanger. Having been thus warmed by heat exchange with theincoming air, the oxygen product is delivered through a pipe 49 andvalve 50 to a suitable storage receptacle.

The apparatus hereinbefore described is an ordinary Claude liquefactionsystem and forms no part of the present invention. Any other systemcapable of performing the same tunes tions can be utilized'for thepurpose of the invention. It is merely necessary in this part of-theapparatus to separate nitrogen from an oxygen liquid containing thekrypton and xenon initially present in the-air.

For the practice of the present invention, an auxiliary column 51 isprovided with trays 52 or the usual form and with a partition 53 torminga lower compartment 54. Apipe '55 delivers liquid from the upperrectifying section of the {auxiliary column 51 to the compartment 54.Liquid oxygen containing krypton and xenon is delivered through a pipe56 controlled by a valve 57 from the compartment 10 of the primarycolumn 5 to a receptacle 58 at the top of the auxiliary column 51'. Thereceptacle 58 has an outlet 59 at its bottom, through which the liquid-flows onto the trays 52.- A liquid level gauge 60 is connected to thereceptacle. 58 to indicate the level of the liquid therein.

In the compartment 54 at the bottom of the auxiliary column 51 a coil 61is provided and is connected by a pipe 62 controlled by a valve 63 tothe pipe 34, so thatliquid from the liquefier 31 at a temperaturesomewhat higher than the liquid in the compartment 54 can be divertedthrough the coil 61 to evaporate that liquid. .The other end of the coilis connected by a pipe 64 controlled by a valve 65 to the pipe 15, theliquid and any vapors remaining of those formed when the liquid divertedfrom pipe 34 passed through valve 62, being thus returned to thecompartment 9 of the primary column 5. At the lower end of theauxiliarycolumn 51 a reduced extension 66 is providedin which the liquidresidue, rich in krypton and xenon, is accumulated and from which it iswithdrawn through a pipe 67 controlled by a valve 68. The liquid can beevaporated and treated for further purification in any suitableapparatus (not shown). A liquid level gauge 69 is connected to thebottom of the extension 66 and to the compartment 54, so that theoperator may observe the level of the liquid in the compartment 54.

All of the apparatus hereinbefore described is enclosed in suitableinsulation to prevent loss of cold during the operation. The liquidlevel gauges 60 and 69 project through the insulation so that they arevisible to the operator.

- -In' operating the apparatus in accordance with the invention, theprimary column 5 produces continuously liquid oxygen containing kryptonand xenon which accumulates in the compartment 120 10 at the bottom ofthe column. This liquid is withdrawn through the pipe 56 and valve 5'7and is delivered to the top of the auxiliary column 51. The liquid ispermitted to flow into the auxiliary column for a limited period, forexample 125 an hour, more or less. The flow or liquid through the pipe56 is then stopped. Meanwhile, some vaporization occurs in thecompartment 10 and the vapor is withdrawn through the pipe 22. Owing tothe difference in boiling points of oxygen and of krypton and xenon,only a small part of the krypton and xenon escapes through the pipe 22and thence through the pipe 43 to the oxygen storage receptacle.

In the auxiliary rectification cycle, air, all or 1 part liquid,is'admitted through the pipe 62, to the coil 61, and because of thediflerence in temperatures between the liquid in the coil and the liquidsurrounding the coil, the latter is partially vaporizedand the vaporsrise through the 14k usual openings provided therefor in the partition53 andtrays 52 in contact withthe liquid flowing downwardly on thetrays. As theresult of the rectification, the rising vapors-ar freedfrom krypton and xenon and finally escapeirom' the top of the auxiliarycolumn into. the pipe 43 by which they are withdrawn as the oxygenproduct of theoperation. The descending liquid is enriched in kryptonand xenon. When the fiow of liquid is stopped by closing the valve 57,

the remaining liquid enriched in krypton and xenon continues toevaporate and is gradually reduced in volume until it fillssubstantially only the extension 66 at the bottom of the auxiliarycolumn, except for such portions of the liquid as may remain on thetrays 52. At this point the liquid residue which is rich in krypton andxenon is withdrawn from the extension 66 through the pipe 67 and valve68 as the krypton and xenon concentrate.

The cycle is then repeated by opening the valve 5'! and permitting afurther portion of the liquid oxygen containing krypton and xenon toflow into the auxiliary column 51. This flow of liquid washes any liquidwhich may remain on the trays 52 into the compartment 54 of theauxiliary column 51. When the rectification in the auxiliary column hasproceeded to the extent hereinbefore indicated, the valve 57 is againclosed, and the liquid is evaporated to produce a residue rich inkrypton and xenon which is again withdrawn.

By the operation as described, the recovery of krypton and xenon fromthe atmosphere is accomplished in a simple, economical and satisfactorymanner. The operation involving the intermittent delivery of the oxygenliquid containing krypton and xenon and final evaporation of the liquidresidue is more effective than a continuous vaporization andrectification of the liquid accumulating in the bottom of the primarycolumn 5. The reduced extension at the bottom of the auxiliary column isan important improvement, since it facilitates the collection of thesmall quantity of residual liquid rich in krypton and xenon. It ispossible to recover by the procedure described 70% or more of thekrypton and xenon I originally present in the air treated.

Various changes may be made in the arrangement of the apparatus and intheprocedure as described, without departing from the invention orsacrificing any of the advantages thereof.

I claim:

1. The method of recovering krypton and xenon from the atmosphere whichcomprises separating by liquefaction and rectification the principalconstituents of the air, nitrogen and oxygen, collecting the oxygen as aliquid containing substantially all of the krypton and xenon initiallyincluded in the air, subjecting this liquid to an auxiliaryrectification with vapors produced therefrom, thereby enriching theliquid in krypton and xenon, discharging the vapors consistingsubstantially of oxygen, cutting oil the supply of oxygen liquidcontaining krypton and xenon from the primary rectification, subjectingthe enriched liquid product of the auxiliary rectification to furtherevaporation, withdrawing the accumulated liquid residue, thenintroducing another portion of the oxygen liquid containing krypton andxenon and repeating the cycle.

2. The method of recovering krypton and xenon from the atmosphere whichcomprises separating by liquefaction and rectification the principalconstituents of the air, nitrogen and oxygen, collecting the oxygen as aliquid containing substantially all of the krypton and xenon initiallyincluded in the air, subjecting this liquid to an auxiliaryrectification with vapors produced therefrom, thereby enriching theliquid-in krypton and and xenon, discharging the vapors consistingsubstantially of oxygen, cutting lOfi the supply of oxygen liquidcontaining krypton and xenon'from the primary rectification, subjectingthe enriched liquid product of the auxiliary rectification to furtherevaporation while preventing loss of krypton and xenon by reasonthereof, withdrawing the accumulated liquid residue, then introducinganother portion of the oxygen liquid containing krypton and xenon andrepeating the cycle.

'woLco'rr DENNIS.

